Flexxaire Manufacturing Inc. of Edmonton, Canada, manufactures a variable pitch fan. This fan is predominantly used to cool industrial diesel engines. The pitch of the blades are adjusted to control both the direction and the amount of airflow generated by the fan. The primary benefits of controlling the airflow are two fold: Reversing the airflow allows debris to be blown off the radiator to reduce or eliminate overheating caused by clogged radiator. The second primary benefit is the ability to provide airflow on demand. This allows the fan to only blow as much air as required to cool the engine thereby reducing the parasitic horsepower draw of the fan resulting in either fuel savings or higher machine productivity as the saved horsepower becomes available for productivity increase. Examples of Flexxaire fans are shown in FIGS. 1 and 2 of U.S. Pat. No. 7,229,250 issued Jun. 12, 2007.
Flexxaire has offered fans where the actual pitch is not measured or known, but the pitch control system monitors fluid temperatures and adjusts pitch as follows: If any temperature is higher than desired, increase the pitch in stepped increase. If all temperatures are below the desired temperature, decrease the pitch in a stepped amount. If all temperatures are within acceptable parameters do not adjust pitch. This control scheme is a closed loop control scheme where the control is closed on fluid temperatures and the pitch is not known. A design of a Flexxaire fan with a pitch change system is shown in US published application no. 20090196747 published Aug. 6, 2009.
This system has worked effectively, but there are a number of deficiencies that can only be resolved when actual pitch is known, and therefore a pitch sensor is desirable. The challenge with developing a pitch sensor is that the entire fan is rotating at high speeds except for the shaft on the rotary union. Therefore to measure the pitch of the rotating fan presents challenges of obtaining information for a rotating frame of reference to a stationary frame.